Even though I like cats, I do feel calls to shut the line down until it is found are unreasonable. Cats are very hardy creatures, and more than capable of surviving in the wild if needs be. And they are equally capable for getting themselves out of some very sticky situations when they have to.
The owners says they can hear the cat calling, but we have to remember that cats have only developed the meow for us humans, or more to the point to attract our attention for food or assistance. A cat meowing is not necessarily a sign of distress, it could just be thinking it might be easier to get a human to help out in the same way that they sometimes get "stuck" up trees and call to passing humans to help. But you leave one long enough and it will almost always find a way down. So the cat in question is probably only calling because its aware of humans being around. So long as it is not severely injured, it will make its own way out when it gets hungry. However cats can also be fickle, and not returning straight home is not necessarily a sign that it is still stuck, it just might be that it is exploring new ground and enjoying an expansion of it's empire.